1. Technical Field
The present invention relates to a keypad data entry devices and more specifically to keypad devices that have automatically dimmable lettering and or legends based on ambient light levels.
2. Background Art
It is known to those skilled in the art, that keypad devices are available in a variety of foreground and background colors. For example, FIG. 1 shows two possible combinations of a faceplate background color and a key legend foreground color. The white keypad device 10 has a white colored faceplate 101 and white colored key capsules 102 with black legends 103. The black keypad device 15 has a black colored faceplate 151 and black colored key capsules 152 with white legends 153. According to the prior art, a white keypad device 10 and a black keypad device 15 with automatic dimming functionality are not interchangeable even if the faceplate and keys were replaceable because the automatic dimming curves are dependent on the corresponding background and foreground colors.
It is common to backlight lighter color transparent or translucent foregrounds on darker color backgrounds by increasing the backlight level intensity as the ambient light level increases. However, this technique will not work in the case of a light color background such as white with a darker colored backlit transparent or translucent foreground color such as gray. In this case, increasing the backlight intensity as the ambient light increases will create a wide range of ambient light levels during which the foreground color vanishes. This optical effect is well known and techniques of this type have been used in magician's tricks and military camouflage. This is illustrated in FIG. 2. When a backlight is combined with reflected ambient light from the translucent plastic foreground to approximate the amount of ambient light that would be reflected from the light background (e.g. white paint at 90% reflectivity), the legend is ‘washed out’.
In addition, a homeowner wishing to change the color theme has no choice but to replace an entire keypad device. Also, service technicians need to carry spare parts of each entire keypad device.
To solve the aforementioned problems associated with carrying extra spares, etc., the present invention is an automatically dimmable keypad device which stores a number of dimming curves corresponding to various combinations of background and foreground colors.